The invention relates to a device for detecting and storing digital pictures comprising an image detector for the generation of digital picture data and a picture processing device with a picture data memory.
Furthermore the invention relates to a method of detecting, processing and storing digital pictures with a digital camera.
It is known to take pictures with a digital camera, whereby digital picture data are generated, to process these digital picture data and to store the picture data in a data memory. Such digital cameras usually have a CCD image detector. CCD (charge coupled device) image detectors are well known in the literature, and, for example, described in the books “Laserspektroskopie” by Wolfgang Demtröder, 3rd Edition, Springer-Verlag Berlin Heidelberg New York or Bergmann Schaefer “Lehrbuch der Experinmentalphysik”, Festkörper (solid state bodies), Volume 6, de Gruiter Verlag.
Such CCD image detectors consist of a plurality of CCD sensors assembled in a matrix. Each CCD sensor provides color or gray value information for one picture element (pixel). This information is read as digital number. Good CCD sensors have a dynamic range of 10 bit or more. In principle, at least 210 color or gray values can be represented with such a system. Current picture display systems usually operate with only 8 bit gray values. Therefore, the 256 gray values which can be displayed with such a system are not sufficient to make full use of the complete dynamic range of the CCD sensors.
Such image detecting and picture processing systems are used in traffic monitoring installations operating with a digital camera. Traffic monitoring installations serve to detect violations of traffic regulations, such as speeding or passing a red traffic light, by a vehicle driver. Such traffic monitoring installations would provide an optimal picture for prosecution of the violation, if both the driver in the comparatively dark passenger compartment of the vehicle and the bright license plate could be well recognized. This is not possible with the presently available image detecting systems. Either the dark portions of the pictures are too dark, if the picture of the license plate is optimally visible, or the bright portions of the pictures are too bright, if the driver is optimally visible in the dark passenger compartment. Thus, when a vehicle is photographed with a digital camera, either the driver in the dark passenger compartment cannot be recognized clearly, or the bright license plate is subject to blanketing and cannot be read, depending on the utilized partial brightness range of the whole dynamic range of the CCD image detector. This results often in considerable problems in particular with the subsequent picture processing. The pictures have to be unambiguously identified both with respect to the driver and to the license plate, in order to serve as evidence in court.